linux-kernel - Re: [PATCH 9/9] reset: gpio: use software nodes to setup the GPIO lookup

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Message-ID: <CAMRc=MdS778OB+CcFp_Q8S9by+ua1E_o2E1wDpjB_WJKzT5=zw@mail.gmail.com>
Date: Fri, 10 Oct 2025 16:07:52 +0200
From: Bartosz Golaszewski <brgl@...ev.pl>
To: Philipp Zabel <p.zabel@...gutronix.de>
Cc: Linus Walleij <linus.walleij@...aro.org>, 
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>, Daniel Scally <djrscally@...il.com>, 
	Heikki Krogerus <heikki.krogerus@...ux.intel.com>, 
	Sakari Ailus <sakari.ailus@...ux.intel.com>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, "Rafael J. Wysocki" <rafael@...nel.org>, 
	Danilo Krummrich <dakr@...nel.org>, Krzysztof Kozlowski <krzk@...nel.org>, linux-gpio@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org, 
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH 9/9] reset: gpio: use software nodes to setup the GPIO lookup

On Mon, Oct 6, 2025 at 5:55 PM Philipp Zabel <p.zabel@...gutronix.de> wrote:
>
> On Mo, 2025-10-06 at 15:00 +0200, Bartosz Golaszewski wrote:
> > From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> >
> > GPIO machine lookup is a nice mechanism for associating GPIOs with
> > consumers if we don't know what kind of device the GPIO provider is or
> > when it will become available. However in the case of the reset-gpio, we
> > are already holding a reference to the device and so can reference its
> > firmware node. Let's setup a software node that references the relevant
> > GPIO and attach it to the auxiliary device we're creating.
> >
> > Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> > ---
> >  drivers/reset/core.c | 132 ++++++++++++++++++++++++++++++---------------------
> >  1 file changed, 78 insertions(+), 54 deletions(-)
> >
> > diff --git a/drivers/reset/core.c b/drivers/reset/core.c
> > index c9f13020ca3a7b9273488497a7d4240d0af762b0..b3e6ba7a9c3d756d2e30dc20edda9c02b624aefd 100644
> > --- a/drivers/reset/core.c
> > +++ b/drivers/reset/core.c
> [...]
> > @@ -849,52 +852,45 @@ static void __reset_control_put_internal(struct reset_control *rstc)
> >       kref_put(&rstc->refcnt, __reset_control_release);
> >  }
> >
> > -static int __reset_add_reset_gpio_lookup(struct gpio_device *gdev, int id,
> > -                                      struct device_node *np,
> > -                                      unsigned int gpio,
> > -                                      unsigned int of_flags)
> > +static void reset_aux_device_release(struct device *dev)
>
> static void reset_gpio_aux_device_release(struct device *dev)
>
> [...]
> > @@ -903,8 +899,10 @@ static int __reset_add_reset_gpio_lookup(struct gpio_device *gdev, int id,
> >  static int __reset_add_reset_gpio_device(const struct of_phandle_args *args)
> >  {
> >       struct reset_gpio_lookup *rgpio_dev;
> > -     struct auxiliary_device *adev;
> > -     int id, ret;
> > +     struct property_entry properties[2];
>
> It would be nice if this could be initialized instead of the memset() +
> assignment below. Maybe splitting the function will make this more
> convenient.
>
> > +     unsigned int offset, of_flags;
> > +     struct device *parent;
> > +     int id, ret, lflags;
>
> Should this be unsigned int, or enum gpio_lookup_flags?

It's represented as u64 in struct software_node_ref_args so unsigned
int works fine.

>
> >
> >       /*
> >        * Currently only #gpio-cells=2 is supported with the meaning of:
> > @@ -915,11 +913,30 @@ static int __reset_add_reset_gpio_device(const struct of_phandle_args *args)
> >       if (args->args_count != 2)
> >               return -ENOENT;
> >
> > +     offset = args->args[0];
> > +     of_flags = args->args[1];
> > +
> > +     /*
> > +      * Later we map GPIO flags between OF and Linux, however not all
> > +      * constants from include/dt-bindings/gpio/gpio.h and
> > +      * include/linux/gpio/machine.h match each other.
> > +      *
> > +      * FIXME: Find a better way of translating OF flags to GPIO lookup
> > +      * flags.
> > +      */
> > +     if (of_flags > GPIO_ACTIVE_LOW) {
> > +             pr_err("reset-gpio code does not support GPIO flags %u for GPIO %u\n",
> > +                    of_flags, offset);
> > +             return -EINVAL;
> > +     }
> > +
> >       struct gpio_device *gdev __free(gpio_device_put) =
> >               gpio_device_find_by_fwnode(of_fwnode_handle(args->np));
> >       if (!gdev)
> >               return -EPROBE_DEFER;
> >
> > +     parent = gpio_device_to_device(gdev);
> > +
> >       /*
> >        * Registering reset-gpio device might cause immediate
> >        * bind, resulting in its probe() registering new reset controller thus
> > @@ -936,6 +953,13 @@ static int __reset_add_reset_gpio_device(const struct of_phandle_args *args)
> >               }
> >       }
> >
> > +     lflags = GPIO_PERSISTENT | (of_flags & GPIO_ACTIVE_LOW);
>
> Could we get an of_flags_to_gpio_lookup_flags() kind of helper for
> this?
>

I have this on my TODO list but it's not straightforward. The defines
under include/dt-bindings/gpio/gpio.h and include/linux/gpio/machine.h
are named the same in some instances but have different values.
Additionally gpiolib-of.c (re)defines its own of_gpio_flags with the
values taken from the dt bindings. It's a mess to untangle. I will get
there but not just yet, hence the FIXME comment.

Bart